Electro-magnetophoresis display

ABSTRACT

The present invention is directed to an electro-magnetophoresis display having either the traditional up/down or dual switching mode. The display cells are filled with an electro-magnetophoretic dispersion comprising particles suspended in a solvent and the particles are both charged and magnetized.  
     The display of the invention prevents undesired movement of the particles in the cells. The magnetic force generated by the magnetic layer(s) eliminates the need to provide cells with a threshold voltage high enough to avoid the cross talk and/or cross bias effects. In addition, the dual switching mode allows the particles to move in the up/down direction as well as the planar direction, thus providing a multicolor display of high color quality at very low cost.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication Serial No. 60/375,299, filed Apr. 23, 2002, the content ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The electrophoretic display (EPD or EPID) is a non-emissivedevice based on the electrophoresis phenomenon of charged pigmentparticles suspended in a solvent. It was first proposed in 1969. Thedisplay typically comprises two plates with electrodes placed opposingeach other, separated by spacers. One of the electrodes is usuallytransparent. A suspension composed of a colored solvent and chargedpigment particles, is enclosed between the two plates. When a voltagedifference is imposed between the two electrodes, the pigment particlesmigrate to one side and then either the color of the pigment or thecolor of the solvent can be seen according to the polarity of thevoltage difference.

[0003] There are several different types of EPDs. In the partition typeEPD (see M. A. Hopper and V. Novotny, IEEE Trans. Electr. Dev.,26(81):1148-1152 (1979)), there are partitions between the twoelectrodes for dividing the space into smaller cells in order to preventundesired movements of particles, such as sedimentation. Themicrocapsule type EPD (as described in U.S. Pat. Nos. 5,961,804 and5,930,026) has a substantially two dimensional arrangement ofmicrocapsules each having therein an electrophoretic composition of adielectric fluid and a suspension of charged pigment particles thatvisually contrast with the dielectric solvent. Another type of EPD (seeU.S. Pat. No. 3,612,758) has electrophoretic cells that are formed fromparallel line reservoirs. The channel-like electrophoretic cells arecovered with, and in electrical contact with, transparent conductors. Alayer of transparent glass from which side the panel is viewed overliesthe transparent conductors.

[0004] An improved EPD technology was disclosed in co-pendingapplications, U.S. Ser. No. 09/518,488, filed on Mar. 3, 2000(corresponding to WO 01/67170), U.S. Ser. No. 09/759,212, filed on Jan.11, 2001 (corresponding to WO 02/56097), U.S. Ser. No. 09/606,654, filedon Jun. 28, 2000 (corresponding to WO 02/01281) and U.S. Ser. No.09/784,972, filed on Feb. 15, 2001 (corresponding to WO 02/65215), allof which are incorporated herein by reference. The improved EPDcomprises closed cells formed from microcups of well-defined shape, sizeand aspect ratio, filled with charged pigment particles dispersed in adielectric solvent, and sealed with a polymeric sealing layer.

[0005] All of these EPDs may be driven by a passive matrix system. For atypical passive matrix system, there are row electrodes on the top sideand column electrodes on the bottom side of the cells. The top rowelectrodes and the bottom column electrodes are perpendicular to eachother. However, there are two well-known problems which are associatedwith EPDs driven by a passive matrix system: cross-talk and cross-bias.Cross-talk occurs when the particles of a cell (pixel) are biased by theelectric field of a neighboring cell (pixel). FIG. 1 provides anexample. The bias voltage of the cell A drives the positively chargedparticles towards the bottom of the cell. Since cell B has no voltagebias, the positively charged particles in cell B are expected to remainat the top of the cell. However, if the two cells, A and B, are close toeach other, the top electrode voltage of cell B (30V) and the bottomelectrode voltage of cell A (0V) create a cross talk electric fieldwhich forces some of the particles in cell B to move downwards. Wideningthe distance between adjacent cells may reduce such a crosstalk effectbut the resolution of the display will also be reduced.

[0006] The cross talk problem may be lessened if a cell has asignificantly high threshold voltage. The threshold voltage, in thecontext of the present invention, is defined to be the minimum (oronset) bias voltage required to move particles away from their currentposition. If the cells have a sufficiently high threshold voltage, thecross-talk may be reduced or eliminated without sacrificing theresolution of the display. A high threshold voltage may be achieved by,for example, increasing the particle-particle interaction or theparticle electrode interaction in the electrophoretic cells.Unfortunately, most approaches to increase the threshold voltage tend toresult in a significant increase in display driving voltage or adecrease in switching rate.

[0007] In addition to the crosstalk by neighboring cells, cross bias isalso possible in a passive matrix display. The voltage applied to acolumn electrode not only provides the driving bias for the cell on thescanning row, but it also affects the bias across the non-scanning cellson the same column. This undesired bias may force the particles of anon-scanning cell to migrate to the opposite electrode. This results inchanges in image density and a significant deterioration of the displaycontrast. A system having gating electrodes was disclosed in U.S. Pat.Nos. 4,655,897 and 5,177,476 (assigned to Copytele, Inc.) to provideEPDs capable of high resolution at relative high driving voltage using atwo layer electrode structure, one of which layers serves as a gatingelectrode. Although these references teach how the threshold voltage maybe raised by the use of gating electrodes, the cost for fabricating thetwo electrode layers is extremely high due to the complexity of thestructure and the low yield rate. In addition, in this type of EPDs, theelectrodes are exposed to the solvent, which could result in anundesired electroplating effect and deterioration in the displayoperation longevity.

[0008] The in-plane switched EPD device disclosed in U.S. Pat. No.6,239,896 uses a magnetic bottom substrate to attract the magneticparticles and provide a threshold effect against the undesirableparticle movement. The row and column electrodes are implemented on thebottom layers forming the driving dot matrix. The in-plane electrodesare significantly more difficult to manufacture than the normal up-downelectrodes, particularly for high resolution displays. The switchingrate of the in-plane displays are slower at a comparable operationvoltage since the distance between electrodes in the in-plane switchingmode is typically larger than the normal up-down mode. Moreover, thecolor saturation of a color display will be poor due to the lack ofeither true white or true black state.

[0009] Therefore, there is still a need for an electrophoretic displayin which the cross talk and cross bias effects will not cause adegradation of display performance, even if cells having a relativelylow intrinsic threshold voltage are used.

SUMMARY OF THE INVENTION

[0010] The present invention has two aspects. The first aspect isdirected to an electro-magnetophoresis display having the traditionalup/down switching mode. The display comprises one top row electrodelayer, one bottom column electrode layer and an array of cellssandwiched between the two electrode layers. In one embodiment of thisaspect of the invention, one switchable magnetic layer is placedunderneath the bottom electrode layer. In another embodiment, there aretwo switchable magnetic layers, one placed on top of the top rowelectrode layer and the other placed underneath the bottom electrodelayer. In a third embodiment, there is one permanent magnetic layerplaced on top of the top row electrode layer, and one switchablemagnetic layer placed underneath the bottom electrode layer. In a fourthembodiment, there is one permanent magnetic layer placed on top of thetop row electrode layer, and one permanent magnetic layer placedunderneath the bottom electrode layer.

[0011] The second aspect of the invention is directed to a dual modeelectro-magnetophoresis display. The display also comprises one top rowelectrode layer, one bottom column electrode layer and an array of cellssandwiched between the two layers. The bottom column electrode layer foreach cell, however, comprises one center electrode and two sideelectrodes, which are placed on the two sides of the center electrode.In one embodiment of this aspect of the invention, there is a switchablemagnetic layer placed underneath the bottom column electrode layer. In asecond embodiment, there are two switchable magnetic layers, one ofwhich is placed on top of the top row electrode layer and the other isplaced underneath the bottom column electrode layer. In a thirdembodiment, there is one permanent magnetic layer placed on top of thetop row electrode layer, and one switchable magnetic layer placedunderneath the bottom electrode layer. In a fourth embodiment, there isone permanent magnetic layer placed on top of the top row electrodelayer and one permanent magnetic layer placed underneath the bottomelectrode layer.

[0012] In all embodiments of the invention, the top side is the viewingside and therefore at least the top row electrode layer and the topmagnetic layer (if present) are transparent.

[0013] The cells are filled with an electromagnetophoretic fluidcomprising charged magnetic particles dispersed in a contrast-coloreddielectric solvent. When the charged magnetic particles are attracted tothe viewing side, the color (the primary color) of the magneticparticles is seen. In contrast, the color of the solvent or its additivecolor with the background is seen when they are attracted away from theviewing side. The solvent may be colored by a pigment or dye.

[0014] The design of the present invention has many advantages. First ofall, it prevents undesired movement of the charged particles in thecells. The magnetic force generated by the magnetic layer(s) eliminatesthe need to provide cells with a threshold voltage high enough to avoidthe cross-talk and/or cross-bias effects. In addition, the dualswitching mode allows the particles to move in the up/down direction aswell as the planar direction, thus providing a multicolor display ofhigh color quality at very low cost.

[0015] These and other features and advantages of the present inventionwill be presented in more detail in the following detailed descriptionand the accompanying figures, which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings,wherein like reference numerals designate like structural elements, andin which:

[0017]FIG. 1 illustrates the “cross-talk” phenomenon of an EPD.

[0018]FIGS. 2A and 2B are side and top views of anelectromagnetophoretic display (EMPD) of the invention having thetraditional up/down switching mode and one switchable magnetic layer.

[0019]FIGS. 3A and 3B are side and top views of an EMPD device of theinvention having the traditional up/down switching mode and two magneticlayers.

[0020]FIGS. 4A and 4B are side and top views of an EMPD device of theinvention having a dual mode and one switchable magnetic layer.

[0021]FIGS. 5A and 5B are side and top views of an EMPD device of theinvention having a dual mode and two magnetic layers.

[0022]FIGS. 6A, 6B and 6C illustrate possible structures for generatingmagnetic field.

[0023]FIGS. 7A and 7B illustrate a 2×3 passive matrix of an EMPD deviceof FIG. 2A.

[0024] FIGS. 8A-8C illustrate an EMPD device capable of dual modeswitching.

DETAILED DESCRIPTION OF THE INVENTION

[0025] A detailed description of representative embodiments of theinvention is provided below. While the invention is described inconjunction with representative embodiments, it should be understoodthat the invention is not limited to these embodiments. In order to meetthe specific requirements of a particular EMPD, the design anddimensions of the features may vary and all such variations are withinthe scope of the present invention. To illustrate this invention,numerous specific details are set forth in the following description.The present invention may be practiced according to the claims withoutsome or all of these specific details. For the purpose of clarity,technical material that is known in the technical fields related to theinvention has not been described in detail so that the present inventionis not unnecessarily obscured.

[0026] I. Definitions

[0027] Unless defined otherwise in this specification, all technicalterms are used herein according to their conventional definitions asthey are commonly used and understood by those of ordinary skill in theart.

[0028] The term “threshold voltage” in the context of the presentinvention is defined as the minimum (or onset) bias voltage required tomove particles away from their current position. The particle thresholdeffect is one of the most important characteristics of theelectrophoretic display and is a function of the particle-particle,particle-solvent and particle electrode interactions.

[0029] The term “driving voltage”, in the context of the presentdisclosure, is defined as the bias voltage applied to change the colorstate of a cell, such as by driving the particles in the cell from aninitial position at or near one electrode to an end position at or nearanother electrode. The driving voltage used in a particular applicationmust be sufficient to cause the color state of the cell to change withinthe required performance parameters of the application, including asmeasured by such parameters as the time it takes for the statetransition to be completed.

[0030] The term “scanning row” in a passive matrix display is a row inthe display that is currently being updated or addressed.

[0031] The term “non-scanned row” is a row that has not been updated oraddressed.

[0032] The term “scanned row” is a row that has been updated oraddressed.

[0033] For a cell in a scanning row, the driving voltage (i.e., biasconditions) should either drive the particles to a desired new locationor maintain the particles at the same location. For a cell on either ascanned row or non-scanned row, the driving voltage should maintain theparticles at the same location even if the bottom column driver voltage(i.e., the voltage applied to the column electrode associated with thecell) changes, such as may occur if a cell in the scanning row in thatcolumn is being switched (i.e., under a cross bias condition). A passivematrix electrophoretic display is usually updated (“scanned”) one row ata time, with the goal being to update the cells of the scanning rowwhile leaving the cells in the scanned and non-scanned rows unchanged.

[0034] The term “positive bias”, in the context of the presentdisclosure, is defined as a bias that tends to cause positively chargedparticles to migrate downwards (i.e., upper electrode at higherpotential than lower electrode).

[0035] The term “negative bias”, in the context of the presentdisclosure, is defined as a bias that tends to cause positively chargedparticles to migrate upwards (i.e., lower electrode at higher potentialthan upper electrode).

[0036] In the context of the present invention, the magnetic forcegenerated between the particles and the magnetic layer(s) may bereferred to as “magnetic force TM” or “magnetic force BM”. When there isonly one bottom magnetic layer, “magnetic force TM” is the magneticforce formed between the magnetic layer and the particles when theparticles are at the top of a cell and “magnetic force BM” is themagnetic force formed between the magnetic layer and the particles whenthe particles are at the bottom of a cell. Because of the distancebetween the bottom magnetic layer and the top of the display, “magneticforce BM” is always greater than “magnetic force TM” when there is onlyone bottom magnetic layer. In the case of two magnetic layers one ofwhich is at the top of a cell and the other is at the bottom of thecell, particles on the top of the cell form a “magnetic force TM” withthe top magnetic layer, and particles at the bottom form a “magneticforce BM” with the bottom magnetic layer.

[0037] In the context of the present invention, each of the magneticforces TM and BM may be converted to a bias voltage, which attracts theparticles with a force equivalent to the magnetic force. If the magneticforce is expressed as

Fm=M·∇|B|

[0038] in which M is the magnitization of the magnetic particles and∇|B| is the gradient of the magnetic field, the equivalent bias voltageis then

Vm=Fm·d/q

[0039] in which q is the charge of the particle and d is the distancebetween the top and the bottom electrodes. Following this conversion,Vtm represents the equivalent bias voltage of the magnetic force TMwhereas Vbm represents the equivalent bias voltage of the magnetic forceBM.

[0040] The magnetic fields generated by the top and the bottomelectromagnets are in the opposite direction, therefore particles at thetop of the cell are attracted by the top magnetic layer and rejected bythe bottom magnetic layer, particles at the bottom of the cell areattracted by the bottom magnetic layer and rejected by the top magneticlayer. In either scenario, the two magnetic forces assist each other.

[0041] The term “screening effect” means that some particles in a cellmigrate faster than others and arrive at the destination electrodebefore the others. These fast particles actually reduce the strength ofthe electric field and further slow down the slower particles.

[0042] II. Various Designs of the Present Invention

[0043] A. Electro-Magnetophoresis Display Having the Traditional Up/DownSwitching Mode

[0044] In one embodiment, as shown in FIG. 2A, the display comprises atop electrode layer (21) and a bottom electrode layer (22), at least oneof which is transparent (e.g., top electrode layer 21), and a cell (20)positioned between the two layers. The top electrode layer (21)comprises one row electrode (23) and the bottom electrode layer (22)comprises one column electrode (24). A switchable magnetic layer (25) isplaced underneath the bottom electrode layer. The top row electrodes andbottom column electrodes are cross (preferably perpendicular) to eachother and the magnetic layer is aligned with the top row electrode layer(21/23) (see FIG. 2B). The display cell (20) comprises charged magneticparticles (26) dispersed in a dielectric solvent (27). In oneembodiment, the particles (26) are positively charged.

[0045] An alternative embodiment is shown in FIG. 3A, in which the basicdesign is similar to that of the embodiment of FIG. 2A except that thereare two switchable magnetic layers (35 a and 35 b), one (35 a) on top ofthe top row electrode layer (31) and the other one (35 b) underneath thebottom column electrode layer (32), and the two magnetic layers arealigned with the row electrodes (31/33) as shown in FIG. 3B.

[0046] The basic design of a third alternative embodiment is similar tothat of the embodiment of FIG. 3A except that the top magnetic layer (35a) on top of the top row electrode layer is permanent and the magneticlayer (35 b) underneath the bottom column electrode layer is switchable.

[0047] The basic design of a fourth alternative embodiment is alsosimilar to that of the embodiment of FIG. 3A except that both magneticlayers (35 a and 35 b) are permanent.

[0048] B. Electro-Magnetophoresis Display Having a Dual Switching Mode

[0049] In one embodiment, as shown in FIG. 4A, the display comprises atop electrode layer (41) and a bottom electrode layer (42), at least theone on the viewing side is transparent (the top electrode layer 41), anda cell (40) positioned between the two layers. The top electrode layer(41) comprises one row electrode (43). The bottom electrode layer (42)comprises one center electrode (44) and two side electrodes (45) placedon the two sides of the center electrode. There are gaps (46) separatingthe center electrode from the side electrodes. A switchable magneticlayer (47) is placed underneath the bottom electrode layer (42). The toprow electrodes and bottom column electrodes are perpendicular to eachother and the magnetic layer (47) is aligned with the top row electrodelayer (41) (see FIG. 4B). The display cell (40) comprises chargedmagnetic particles (48) in a dielectric solvent (49). In one embodiment,the particles (48) are positively charged.

[0050] An alternative embodiment is shown in FIG. 5A, in which the basicdesign is similar to that of the embodiment of FIG. 4A except that thereare two switchable magnetic layers (57 a and 57 b), one (57 a) on top ofthe top row electrode layer (51) and the other one (57 b) underneath thebottom column electrode layer (52) and the two magnetic layers arealigned with the top row electrodes (see FIG. 5B).

[0051] The basic design of a third alternative embodiment is similar tothat of the embodiment of FIG. 5A except that the top magnetic layer (57a) on top of the top row electrode layer is permanent and the bottommagnetic layer (57 b) underneath the bottom column electrode layer isswitchable.

[0052] The basic design of a fourth embodiment is also similar to thatof the embodiment of FIG. 5A except that both magnetic layers (57 a and57 b) are permanent.

[0053] The displays generally may be manufactured according to themethods known in the art. The scope of the invention encompasses theconventional displays (i.e., the partition type display as shown in U.S.Pat. Nos. 3,668,106 and 3,612,758), the displays manufactured by themicrocup technology (as disclosed in WO 01/67170 and WO 02/01281) andthe displays manufactured by the microencapsulation technology (asdisclosed in U.S. Pat. Nos. 5,961,804 and 5,930,026). In the case of themicrocup-type displays, the display cells are of well-defined size,shape and aspect ratio, and are individually sealed, preferably with apolymeric sealing layer.

[0054] The magnetic particles may be dispersed by any of the well-knownmethods, including grinding, milling, attriting, microfluidizing andultrasonic techniques. For example, magnetic particles in the form of afine powder are added to the suspending solvent and the resultingmixture is ball milled or attrited for several hours to break up thehighly agglomerated dry pigment powder into primary particles. Low vaporpressure, non-hygroscopic solvents are preferred for the magnetophoreticor electromagnetophoretic fluid. Examples of useful solvents includehydrocarbons such as decahydronaphthalene (DECALIN),5-ethylidene-2-norbornene, fatty oils, paraffin oil, aromatichydrocarbons such as toluene, xylene, phenylxylylethane, dodecylbenzeneand alkylnaphthalene, low viscosity polyethers such as polypropyleneglycols and block copolymers of ethylene glycol and propylene glycols,low viscosity silicone oils, alkyl or alkylaryl esters and ketones,halogenated solvents such as perfluorodecalin, perfluorotoluene,perfluoroxylene, dichlorobenzotrifluoride,3,4,5-trichlorobenzotrifluoride, chloropentafluoro-benzene,dichlorononane and pentachlorobenzene, perfluoro solvents such as FC-43,FC-70 and FC-5060 from 3M Company, St. Paul Minn., low molecular weighthalogen containing polymers such as poly(perfluoropropylene oxide) fromTCI America, Portland, Oreg., poly(chlorotrifluoroethylene) such asHalocarbon Oils from Halocarbon Product Corp., River Edge, N.J. andperfluoropolyalkylether such as Galden from Ausimont or Krytox Oils andGreases K-Fluid Series from DuPont, Del. In one preferred embodiment,poly(chlorotrifluoroethylene) is used as a dielectric solvent. Inanother preferred embodiment, poly(perfluoropropylene oxide) is used asa dielectric solvent.

[0055] Sedimentation or creaming of the pigment particles may beeliminated by microencapsulating the particles with suitable polymers tomatch the specific gravity to that of the suspending solvent.Microencapsulation of the pigment particles may be accomplishedchemically or physically. Typical microencapsulation processes includeinterfacial polymerization, in-situ polymerization, phase separation,coacervation, electrostatic coating, spray drying, fluidized bed coatingand solvent evaporation. Well-known procedures for microencapsulationhave been disclosed in Kondo, Microcapsule Processing and Technology,Microencapsulation, Processes and Applications, (I. E. Vandegaer, ed.),Plenum Press, New York, N.Y. (1974), and in Gutcho, Microcapsules andMicroencapsulation Techniques, Nuyes Data Corp., Park Ridge, N.J.(1976), both of which are hereby incorporated by reference.

[0056] Magnetic particles prepared from highly magnetic compounds andmetals or alloys are preferred. Examples of magnetic materials useful inthis invention include gamma ferric oxide, acicular magnetite,cobalt-modified or adsorbed ferric oxide, berthollide ferric oxide,chromium dioxide, metals or alloys such as stainless steel, Fe—Co,Fe—Ni, Fe—Co—Ni, Co—Ni, Co—Cr and Fe—Co—V alloys, organic polyradicalssuch as polymers with organic radicals in the side chain, main-chainconjugated polymers with organic radicals, two dimensional polyradicals,polymers containing paramagnetic metalloporphyrins as side chains andpolymers containing paramagnetic metal ions, e.g., Cu(II), Ni(II),Mn(II) or VO(II), in the main chain. Other useful magnetic materials canbe found in references such as “Magnetic Recording Handbook” by MarvinCamras; Van Norstrand Reinhold Co., (1988); and M. Kanachi “MagneticPolymers” in “Functional Monomers and Polymers”, ed. By K. Takemoto, R.M. Ottenbrite and M. Kamachi; Marcel Dekker, Inc., (1997).

[0057] Specific examples of organic polyradicals include, but notlimited to, those shown in the references identified above and severalU.S. patents (e.g., U.S. Pat. Nos. 4,631,328, 4,594,400, 4,552,928 and4,769,443). Organic polyradicals shown by Kanachi in “Magnetic Polymers”include those containing 2,2,6,6-tetramethylpiperidine-1-oxyl as a sidechain, thermally annealed polyphenylacetylene, those with phenoxy ornitroxy radicals, poly(1,3-phenyleneethynylene) with pendant nitronylnitroxide or t-butylnitroxyl, two-dimensional polymers, such as thatobtained by reacting 1,3,5-triaminobenzene with iodine, those with arepeating unit derived from indigo, those obtained from thecatalyst-free 1,3-dipolar cycloaddition of 1,3-bis-(3-sydnone) andN′,N′-(1,4phenylene)bismaleamide, those containing paramagnetic ionseither in the side chain or in the main chain. Those containingparamagnetic ions in the side chain include those containingtetraphenylporphyrin (TPP) moieties, especially those derived fromparamagnetic metal ions, for example, Cu(II), Ag(II), VO(II) and Co(II),and that derived from the reaction of TPP-Mn(II) and tetracyanoethylenein toluene. Those containing paramagnetic ions in the main chain includea heterobinuclear complexes of Cu(II) and VO(II), an inorganic polymer,MnCu(pbaOH)(H₂O)₃ with regularly alternating magnetic centers, wherepbaOH is 2-hydroxy-1,3-propylenebis(oxamato), polymers composed of2-substituted 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and derivedfrom Cu(II), Ni(II) or Mn(II), linear chain polymers of M(hfac)₂(NIT)Rwhere M is Cu(II), Ni(II) or Mn(II), (NIT)R is2-alkyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and hfac ishexafluoroaceteylacetonate, and three dimensional structures, such as(rad)₂Mn₂[Cu(opba)]₃(DMSO)₂:2H₂O, where rad is2-(4-N-methylpyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,opba is o-phenylenebis(oxamato) and DMSO is dimethyl sulfoxide. Otherpolymeric radical containing compounds, with the identity of the radicaland its location, are those described in U.S. Pat. No. 4,631,328(various dyes [anthraquinone, stilbene, mono-, bis-, tris-azo], sidechain), U.S. Pat. No. 4,594,400 (thioxanthone, side chain), U.S. Pat.No. 4,552,928 (di- and triphenylamine, side chain) and U.S. Pat. No.4,769,443 (piperidine, side chain). Some of these organic polyradicalsmay be prepared by including radical precursors in the prepolymermixture, effecting polymerization and then conversion to the radicals.

[0058] Alternatively, charged pigment (such as TiO₂) particles may bemagnetized by microencapsulating the particles with magnetic materials.The magnetic material may be mixed with, or coated onto, pigmentparticles before (preferred) or after the microencapsulation process.Examples of magnetic materials particularly useful in this case includemetal particles or metallized particles prepared by, for example,sputtering, vacuum deposition, electrodeposition, electroplating, orelectroless plating, and microencapsulating/overcoating with magneticpolymers. Charged metallized particles and charged microcapsulescontaining a mixture of pigments and magnetic particles are the mostpreferred.

[0059] The charged magnetized particles may exhibit a native charge, ormay be charged explicitly using a charge control agent, or may acquire acharge when suspended in the suspending medium. Suitable chargecontrolling agents are well known in the art; they may be polymeric ornon-polymeric in nature, and may also be ionic or non-ionic.

[0060] The switchable magnetic layer is formed of rows of electromagnetfor generating a magnetic field. The magnetic layer is switchable(on/off) by applying or turning off a voltage to the electromagnet. FIG.6A illustrates one useful electromagnet by using electrode structure forgenerating a magnetic field. FIG. 6B illustrates a switchable magneticlayer, which comprises arrays of electromagnet 61. FIG. 6C illustrates atypical electromagnet, which is a solenoid with an iron core 62. Whenthe current is applied to the coil 63, a magnetic field is generated. Apermanent magnetic layer comprises a continuous layer constructed by apermanent magnetic material. One embodiment is a ferrite magnet layercomprising ferrite powder and a polymer binder forming a flexibly orrigidly bonded permanent magnets.

[0061] III. Electro-Magnetophoresis Display Having the TraditionalUp/Down Switching Mode

[0062] (a) Up/Down Switching Mode/One Bottom Magnetic Layer

[0063]FIG. 7A illustrates a 2×3 passive matrix of theelectromagnetophoretic display of FIG. 2A and shows the top view of ageneral 2×3 passive matrix. For the purpose of illustration, it isassumed the driving voltage in this scenario is 30V and the magneticparticles are positively charged. The particles are of the white colorand are dispersed in a colored clear solvent. Thus, when the particlesare at the top, the color of the magnetic particle (white in this case)is seen through the top viewing side. In contrast, the color of solventis seen from the viewing side when the particles are at the bottom. Thegoal in this illustration is to drive two cells A and D to the whitestate and cells B and C to the color state while maintaining E and F atthe reset state, which is the white state.

[0064] In FIG. 7A, row R1 has cells A and B; row R2 has cells C and D;row R3 has cells E and F; column C1 has cells A, C and E; and column C2has cells B, D and F.

[0065] Initially the device is reset to move all particles in all sixcells, A, B, C, D, E and F to the top (thus, the white color is seen).When row R1 is the scanning row and rows R2 and R3 are the non-scannedrows, the magnetic layer underneath rows R1, R2 and R3 are all turnedoff. In addition, the driving voltage of 30V is applied to row R1 and 0Vis applied to rows R2 and R3, and at the same time a voltage of 25V isapplied to column C1 and 0V is applied to column C2.

[0066] Under this driving condition:

[0067] 1) In order for the particles in cell A to remain at the top (seeFIG. 7B-1), the following condition must be met:

“threshold voltage”≧5V

[0068] 2) In cell B (FIG. 7B-2), in order for the particles to move tothe bottom of the cell, the following condition must be met:

30V>“threshold voltage”

[0069] 3) In cells C and E, particles are under 25V negative bias, andin cells D and F, the particles are under 0V bias, therefore theparticles remain at the top of the cell.

[0070] After row R1 is scanned, the scanning takes place at row R2 whilerow R1 becomes the scanned row and row R3 is the non-scanned row. Themagnetic layer underneath R1 is now turned on and the magnetic layersunderneath R2 and R3 are turned off. The driving voltage of 30V isapplied to row R2 and a voltage of 0V is applied to rows R1 and R3. Atthe same time, a voltage of 25V is applied to column C2 and 0V isapplied to column C1.

[0071] Under this driving condition:

[0072] 1) In order for the particles in cell D to remain at the top (seeFIG. 7B-4), the following condition must be met:

“threshold voltage”≧5V

[0073] 2) In cell C (FIG. 7B-3), in order for the particles to move tothe bottom of the cell, the following condition must be met:

30V>“threshold voltage”

[0074] When R2 is being scanned, particles in cells A and B must remainat the locations set during the scanning phase. However, for cells A andB on the scanned row when row R2 is being scanned, the voltages appliedto the row (R1) and column electrodes (C1 and C2) have changed. Inaddition, the magnetic layer under row R1 is now turned on.

[0075] 3) Cell A is under 0V bias (FIG. 7B-5), and therefore in order tomaintain the particles at the top, the following condition must be met:

“threshold voltage”≧Vtm

[0076] 4) Cell B is under a 25 V reverse bias (FIG. 7B-6), and thereforein order to maintain the particles in this cell at the bottom, thefollowing must be met:

“threshold voltage”+Vbm≧25V

[0077] 5) In cell E, particles are under 0V bias, and in cell F theparticles are under 25V negative bias, therefore the particles remain atthe top of the cell.

[0078] It may be concluded from this example that if the material has athreshold voltage of 5V, the magnetic force TM then must be equal to orless than 5V electric field strength and the magnetic force BM must beequal to or greater than 20V electric field strength. In general, Vtm inthis design must be equal to or less than Vbm. As to the exact strengthsof the magnetic forces TM and BM required, they would depend on theparticle threshold voltage, which in turn is dependent on the drivingvoltages applied and the nature of the particles and electrodes.

[0079] (b) Up/Down Switching Mode/Two Switchable Magnetic Layers

[0080] This section illustrates a 2×3 passive matrix of theelectro-magnetophoretic display of FIG. 3A. For the purpose ofillustration, it is also assumed the driving voltage in this scenario is30V. The white particles are positively charged and also magnetized.

[0081] Initially, the device is also reset to move all particles in allsix cells, A, B, C, D, E and F, to the top (thus, the white color isseen).

[0082] When row R1 is the scanning row and rows R2 an R3 are thenon-scanned rows, the top and bottom magnetic layers for rows R1, R2 andR3 are all turned off. In addition, the driving voltage of 30V isapplied to row R1 and 0V is applied to rows R2 and R3, and at the sametime a voltage of 30V is applied to column C1 and 0V is applied tocolumn C2.

[0083] Under this driving condition:

[0084] 1) There is 0V bias in cell A. The magnetic layers of R1 areturned off. The particles in cell A therefore remain at the top becauseof the particle bistability.

[0085] 2) In cell B, in order for the particles to move to the bottomthe cell, the following condition must be met:

30V>“threshold voltage”

[0086] 3) In cells C and E, particles are under 30V negative bias, andin cells D and F, the particles are under 0V bias, therefore theparticles remain at the top of these cells.

[0087] When most of the particles in cells A and B are near or havemigrated to their destinations, both voltages applied to R1 and C1 areset to 0V, and at the same time, both top and bottom magnetic layers ofthe scanning row R1 are turned on. The particles already at the top incell A therefore are attracted by the magnetic field generated betweenthe particles and the top magnetic layer and the particles already atthe bottom in cell B are attracted by the magnetic field generatedbetween the particles and the bottom magnetic layer. As a result, thescreening effect is reduced and the particles are packed tighter andremain at their desired locations.

[0088] After row R1 is scanned, the scanning takes place at row R2 whilerow R1 becomes the scanned row. The magnetic layers (both top andbottom) for row R1 are now turned on and the magnetic layers for rows R2and R3 are all turned off. The driving voltage of 30V is applied to rowR2. A voltage of 15V is applied to row R1 and 0V is applied to R3. Atthe same time, a voltage of 30V is applied to column C2 and 0V isapplied to column C1.

[0089] Under this driving condition:

[0090] 1) There is 0V bias in cell D. The magnetic layers of R2 areturned off. The particles in cell D remain at the top because of theparticle bistability.

[0091] 2) In cell C, in order for the particles to move to the bottom ofthe cell, the following condition must be met:

30V >“threshold voltage”

[0092] When most of the particles are near or have migrated to theirdestinations, the voltages applied to R2 and C2 are set to 0V, and atthe same time, both the top and bottom magnetic layers of R2 are turnedon. The particles already at the top in cell D are attracted by themagnetic field formed between the particles and the top magnetic layerand the particles already at the bottom in cell C are attracted by themagnetic field formed between the particles and the bottom magneticlayer. As a result, the screening effect is reduced and the particlesare packed tighter and remain at the desired locations.

[0093] When row R2 is being scanned, particles in cells A and B mustremain at the desired locations set during the scanning phase. However,for cells A and B on the scanned row when row R2 is being scanned, thevoltages applied to the row (R1) and column electrodes (C1 and C2) havechanged. In addition, both magnetic layers for row R1 are now turned on.

[0094] 3) Cell A is under a 15V reverse bias, and therefore in order tomaintain the particles at the top, the following condition must besatisfied:

“threshold voltage”+Vtm≧15V

[0095] 4) Cell B is also under a 15 V reverse bias, and therefore inorder to maintain the particles in this cell at the bottom, thefollowing condition must be met:

“threshold voltage”+Vbm≧15V

[0096] 5) Cell E is under 0V bias and cell F is under 30V negative bias.The particles in these cells remain at the top of the cells.

[0097] It may be concluded that if the particles have a 5V thresholdvoltage in this design, both the magnetic force TM and the magneticforce BM must be equal to or greater than 10V of electric fieldstrength. In general, both Vtm and Vbm in this design must be greaterthan the threshold voltage and their exact strengths are dependent onthe nature of the particles/electrodes and the driving voltages applied.

[0098] (c) Up/Down Switching Mode/One Permanent Top Magnetic Layer andOne Switchable Bottom Magnetic Layer

[0099] This section illustrates a 2×3 passive matrix of theelectro-magnetophoresis display having one permanent top magnetic layerand one switchable bottom magnetic layer. For the purpose ofillustration, it is also assumed that the driving voltage in thisscenario is 30V and the magnetic particles are positively charged.

[0100] Initially the device is also reset to move all particles in allsix cells, A, B, C, D, E and F, to the top (thus, the white color isseen).

[0101] When row R1 is the scanning row and R2 and R3 are the non-scannedrows, the bottom magnetic layers for rows R1, R2 and R3 are all turnedoff. In addition, the driving voltage of 30V is applied to row R1 and 0Vis applied to rows R2 and R3, and at the same time a voltage of 30V isapplied to column C1 and 0V is applied to column C2.

[0102] Under this driving condition:

[0103] 1) There is 0V bias in cell A. The bottom magnetic layer of R1 isturned off. The particles in cell A therefore remain at the top becauseof the particle bistability and the magnetic force formed between theparticles and the top permanent magnetic layer.

[0104] 2) In cell B, in order for the particles to move to the bottomthe cell, the following condition must be met:

30V>“threshold voltage”+Vtm

[0105] 3) In cells C and E, particles are under 30V negative bias, andin cells D and F, the particles are under 0V bias, therefore theparticles remain at the top of the cell. The magnetic force TM alsoassists in holding the particles in these two cells at the top. Whenmost of the particles in cells A and B are near or have migrated totheir destinations, both voltages applied to R1 and C1 are set to 0V,and at the same time, the bottom magnetic layer of the scanning row R1is turned on. The particles already at the top in cell A therefore areattracted by the magnetic field generated between the particles and thetop permanent magnetic layer and the particles already at the bottom incell B are attracted by the magnetic field generated between theparticles and the bottom switchable magnetic layer. As a result, thescreening effect is reduced and the particles are packed tighter andremain at their desired locations.

[0106] After row R1 is scanned, the scanning takes place at row R2 whilerow R1 becomes the scanned row. The magnetic layer at the bottom of rowR1 is now turned on, and the bottom magnetic layers for rows R2 and R3are turned off. The driving voltage of 30V is applied to row R2. Avoltage of 15V is applied to row R1 and 0V is applied to R3. At the sametime, a voltage of 30V is applied to column C2 and 0V is applied tocolumn C1.

[0107] Under this driving condition:

[0108] 1) There is 0V bias in cell D. The bottom magnetic layer R2 isturned off. The particles in cell D remain at the top because of theparticle bistability and the magnetic force between the particles andthe top permanent magnetic layer.

[0109] 2) In cell C, in order for the particles to move to the bottom ofthe cell, the following condition must be met:

30V>“threshold voltage”+Vtm

[0110] When most of the particles are near or have migrated to theirdestinations, the voltage applied to R2 and C2 are set to 0V, and at thesame time, the bottom magnetic layer of R2 is turned on. The particlesalready at the top in cell D are attracted by the magnetic field formedbetween the particles and the top permanent magnetic layer and theparticles already at the bottom in cell C are attracted by the magneticfield formed between the particles and the bottom switchable magneticlayer. As a result, the screening effect is reduced and the particlesare packed tighter and remain at the desired locations.

[0111] When row R2 is being scanned, particles in cells A and B mustremain at the desired locations set during the scanning phase. However,for cells A and B on the scanned row when row R2 is being scanned, thevoltages applied to the row (R1) and column electrodes (C1 and C2) havechanged. In addition, the bottom magnetic layer for row R1 is now turnedon.

[0112] 3) Cell A is under a 15V reverse bias, and therefore in order tomaintain the particles at the top, the following conditions must besatisfied:

“threshold voltage”+Vtm≧15V

[0113] 4) Cell B is also under a 15 V reverse bias, and therefore inorder to maintain the particles in this cell at the bottom, thefollowing conditions must be met:

“threshold voltage”+Vbm≧15V

[0114] 5) Cell E is under 0V bias and cell F is under 30V negative bias.The particles remain at the top of these two cells. The magnetic forceTM also assists in holding the particles at the top.

[0115] From the illustration of this example, if the particle materialhas a 5V threshold effect, the magnetic force TM must be equal to orgreater than 10V electric field strength and the magnetic force BM mustalso be equal to or greater than 10V electric field strength. Ingeneral, for this design, Vtm and Vbm must be greater than the particlethreshold voltage and their exact strengths are dependent on the natureof the particle/electrode and the driving voltages applied.

[0116] (d) Up/Down Switching Mode/Two Permanent Magnetic Layers

[0117] This section illustrates a 2×3 passive matrix of theelectromagnetophoretic display having two permanent magnetic layers. Forthe purpose of illustration, it is also assumed the driving voltage inthis scenario is 30V. The particles are positively charged and alsomagnetized.

[0118] Initially the device is also reset to move all particles in allsix cells, A, B, C, D, E and F, to the top (thus, the white color isseen).

[0119] When row R1 is the scanning row and rows R2 an R3 are thenon-scanned row, a driving voltage of 30V is applied to row R1 and 0V isapplied to rows R2 and R3, and at the same time a voltage of 30V isapplied to column C1 and 0V is applied to column C2.

[0120] Under this driving condition:

[0121] 1) There is 0V bias in cell A. The particles in cell A thereforeremain at the top because of the particle bistability and the magneticforce between the particles and the top magnetic layer.

[0122] 2) In cell B, in order for the particles to move to the bottomthe cell, the following condition must be met:

30V>“threshold voltage”+Vtm

[0123] 3) In cells C and E, particles are under 30V negative bias, andin cells D and F, the particles are under 0V bias, therefore theparticles remain at the top of these cells. The magnetic force TM alsoassists in holding the particles at the top.

[0124] When most of the particles in cells A and B are near or havemigrated to their destinations, both voltages applied to R1 and C1 areset to 0V. The particles already at the top in cell A therefore areattracted by the magnetic field generated between the particles and thetop permanent magnetic layer and the particles already at the bottom incell B are attracted by the magnetic field generated between theparticles and the bottom permanent magnetic layer. As a result, thescreening effect is reduced and the particles are packed tighter andremain at their desired locations.

[0125] After row R1 is scanned, the scanning takes place at row R2 whilerow R1 becomes the scanned row. The driving voltage of 30V is applied torow R2. A voltage of 15V is applied to row R1 and a voltage of 0V isapplied to R3. At the same time, a voltage of 30V is applied to columnC2 and 0V is applied to column C1.

[0126] Under this driving condition:

[0127] 1) There is 0V bias in cell D. The particles in cell D remain atthe top because of the particle bistability and the magnetic forcebetween the particles and the top magnetic layer.

[0128] 2) In cell C, in order for the particles to move to the bottom ofthe cell, the following condition must be met:

30V>“threshold voltage”+Vtm

[0129] When most of the particles are near or have migrated to theirdestinations, the voltage applied to R2 and C2 are set to 0V. Theparticles at the top in cell D are attracted by the magnetic fieldformed between the particles and the top permanent magnetic layer andthe particles at the bottom in cell C are attracted by the magneticfield formed between the particles and the bottom permanent magneticlayer. As a result, the screening effect is reduced and the particlesare packed tighter and remain at the desired locations.

[0130] When row R2 is being scanned, particles in cells A and B mustremain at the desired locations set during the scanning phase. However,for cells A and B on the scanned row when row R2 is being scanned, thevoltages applied to the row (R1) and column electrodes (C1 and C2) havechanged.

[0131] 3) Cell A is under a 15V reverse bias, and therefore in order tomaintain the particles at the top, the following condition must besatisfied:

“threshold voltage”+Vtm≧15V

[0132] 4) Cell B is also under a 15 V reverse bias, and therefore inorder to maintain the particles in this cell at the bottom, thefollowing condition must be met:

“threshold voltage”+Vbm≧15V

[0133] 5) Cell E is under 0V bias and cell F is under 30V negative bias.The particles remain at the top of these two cells. The magnetic forceTM also assists in holding the particles at the top.

[0134] From this example, it may be concluded that if the particles havea 5V threshold effect, the magnetic force TM must be equal to or greaterthan 10V electric field strength and magnetic force BM must also beequal to or greater than 10V electric field strength. In general, Vtmand Vbm must be greater than the particle threshold voltage and theirexact strengths are dependent on the nature of the particles/electrodesand the driving voltages applied.

[0135] IV. Electro-Magnetophoresis Display Having a Dual Switching Mode

[0136] (a) Dual Switching Mode/One Bottom Switchable Magnetic Layer

[0137] A multi-color display having a dual mode of FIG. 4A isillustrated in this section. For the purpose of illustration, it isassumed that the particles are of the white color and are positivelycharged and also magnetized. The particles are dispersed in a clearcolored solvent and the background of the cells is black. Thus, when theparticles are at the top, the white color is seen through the topviewing side. When the particles are at the bottom, the color of solventis seen and when the particles migrate to the side electrodes, the blackcolor (i.e., background color of the cell) is seen, from the viewingside.

[0138] For demonstration, the driving voltage in this illustration is40V. Initially all top row electrodes are reset to 0V, the bottomelectrodes are reset to 40V and the bottom switchable magnetic layersare turned off. As a result, all particles migrate to the top of thecells resulting in a white color being seen from the viewing side.

[0139] When a row is being scanned (scanning row), a driving voltage of40V is applied to the top row electrode and the magnetic layer of thatrow is turned off.

[0140] When a 40V is applied to both the bottom center electrode and thetwo side electrodes of cell A (see FIG. 8A), there is no positive ornegative bias in this cell. However, because of the particlebistability, the particles remain at the top and a white color is seenthrough the viewing side.

[0141] In cell B of FIG. 8B, a voltage of 10V is applied to both thecenter electrode and the two side electrodes, generating a 30V positivebias, which pull the particles downward and as a result, the color ofthe solvent is seen from the viewing side.

[0142] In cell C of FIG. 8C, a voltage of 40V is applied to the centerelectrode and 10V is applied to the side electrodes and as a result ofthe electric field generated, the particles migrate to the sideelectrodes resulting in the black background color being seen from theviewing side.

[0143] When most of the particles in cells B and C are near or havemigrated to their destinations, the voltages applied to the center andside electrodes of the scanning row are set to 0V. The magnetic layer isnow turned on. The particles at the bottom therefore are attracted bythe magnetic field formed between the particles and the bottom magneticlayer. As a result, the screening effect is reduced and the particlesare packed tighter and remain at the desired locations. For thenon-scanned rows, the bottom magnetic layers are turned off and 0V isapplied to the top row electrodes, which results in all particles biasedto the top of the cells and remaining at the top of the cells.

[0144] After a row is scanned, that row becomes a scanned row while thenext row is being scanned. For a scanned row, the magnetic layerunderneath the bottom electrode layers is turned on, and the scannedcells can be in either white, color or black state. A 0V is applied tothe top row electrode of the scanned row. The voltages for the bottomcolumn electrode and the two side electrodes vary according to thestates being driven on the scanning row, thus generating nine possiblescenarios as illustrated below. The particles in a scanned row shouldremain at their locations set during the scanning phase.

[0145] 1) In cell A of FIG. 8A, 0V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row.

[0146] When the column and side electrodes are all at 40V, in order forthe particles to remain at the top, the following condition must besatisfied:

40V+“threshold voltage≧Vtm

[0147] When the column and side electrodes are all at 10V, in order forthe particles to remain at the top, the following condition must besatisfied:

10V+“threshold voltage≧Vtm

[0148] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain at the top, thefollowing condition must be satisfied:

40V+“threshold voltage”≧Vtm

[0149] 2) In cell B of FIG. 8B, 0V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row.

[0150] When the column and side electrodes are all at 40V, in order forthe particles to remain at the bottom, the following condition must besatisfied:

Vbm+“threshold voltage”≧40V

[0151] When the column and side electrodes are all at 10V, in order forthe particles to remain at the bottom, the following condition must besatisfied:

Vbm+“threshold voltage”≧10V

[0152] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain at the bottom, thefollowing condition must be satisfied:

Vbm+“threshold voltage”≧40V

[0153] 3) In cell C of FIG. 8C, 0V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row.

[0154] When the column and side electrodes are all at 40V, in order forthe particles to remain at the side electrodes, the following conditionmust be satisfied:

Vbm+“threshold voltage”>40V

[0155] When the column and side electrodes are all at 10V, in order forthe particles to remain at the side electrodes, the following conditionmust be satisfied:

Vbm+“threshold voltage”≧10V

[0156] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain at the sideelectrodes, the following condition must be satisfied:

Vbm+“threshold voltage”≧10V

[0157] In this example, the particle material threshold effect and themagnetic field strengths must meet the follow conditions:

Vbm+“threshold voltage”≧40V

10V+“threshold voltage”≧Vtm

[0158] If the particle threshold effect is 5V electric field strength,Vbm must be equal to or greater than 35V and Vtm must be equal to orless than 15V. Therefore in general, the top magnetic force must be lessthan the bottom magnetic force. In practice, their exact strengths maybe determined by the inherent particle threshold effect and the drivingvoltages set.

[0159] (b) Dual Switching Mode/Two Switchable Magnetic Layers

[0160] In the second alternative embodiment, the electro-magnetophoreticdisplay differs from the design of FIG. 4A in that it has one additionalswitchable magnetic layer on top of the top row electrode. The magneticfields generated by the two switchable magnetic layers are in theopposite direction. Therefore, for example, when the magnetic particlesare at the top and they are attracted (pulled) to the top side by thetop magnetic layer, the bottom magnetic layer pushes the particles andassists the particles migrate toward the top side although the magneticforce between the particles and the bottom magnetic layer may benegligible. In this alternative design, initially, all top rowelectrodes are also reset to 0V and all bottom electrodes are reset to40V. During reset, all top magnetic rows are turned on and all bottommagnetic layers are turned off. As a result, all particles move to thetop and a white color is seen from the viewing side.

[0161] When a row is being scanned (scanning row), the driving voltageof 40V is applied to the top row electrode and both the top and bottommagnetic layers are turned off. The voltages applied to the bottomcenter and side electrodes are those shown in FIGS. 8A, 8B and 8C.Consequently, the cells may have varied colors as also shown in FIGS.8A, 8B and 8C.

[0162] When most of the particles are near or have migrated to theirdestinations, the voltages applied to the top row, bottom center andside electrodes of the scanning row are set to 0V. Both the top andbottom magnetic layers are turned on. The particles at the top areattracted by the magnetic field formed between the particles and the topmagnetic layer and the particles at the bottom are attracted by themagnetic field formed between the particles and the bottom magneticlayer. As a result, the screening effect is reduced and the particlesare packed tighter and remain at the desired locations.

[0163] For a non-scanned row, the magnetic layers are turned off and 0Vis applied to the top row electrode, which results in all particlesbiased to the top of the cell and remaining at the top of the cell.

[0164] After a row is scanned, that row becomes a scanned row while thenext row is being scanned. For a scanned row, both the top and thebottom magnetic layers are turned on. A 20V is applied to the top rowelectrode of the scanned row.

[0165] The voltages for the bottom column electrode and the two sideelectrodes vary according to the states being driven on the scanningrow, thus generating nine possible scenarios as illustrated below. Theparticles in a scanned row must remain at their locations set during thescanning phase.

[0166] 1) In cell A of FIG. 8A, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row. When the column and side electrodes are all at 40V,the particles remain at the top of the electrode.

[0167] When the column and side electrodes are all at 10V, in order forthe particles to remain at the top, the following condition must besatisfied:

Vtm+“threshold voltage”≧10V

[0168] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain at the top, thefollowing condition must be satisfied:

Vtm+“threshold voltage”≧10V

[0169] 2) In cell B of FIG. 8B, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row.

[0170] When the column and side electrodes are all at 40V, in order forthe particles to remain at the bottom, the following condition must besatisfied:

Vbm+“threshold voltage”≧20V

[0171] When the column and side electrodes are all at 10V, the particlesremain at the bottom.

[0172] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain covering the bottom,the following condition must be satisfied:

Vbm+“threshold voltage”≧30V

[0173] 3) In cell C of FIG. 8C, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row.

[0174] When the column and side electrodes are all at 40V, in order forthe particles to remain at the side electrodes, the following conditionmust be satisfied:

Vbm+“threshold voltage”≧20V

[0175] When the column and side electrodes are all at 10V, the particlesremain at the side electrodes.

[0176] When the column and side electrodes are set at 10V-40V-10Vrespectively, the particles remain at the side electrodes.

[0177] Considering all above scenarios, the particle material thresholdeffect and the magnetic field strengths must meet the follow conditions:

Vbm+“threshold voltage”≧30V

Vtm+“threshold voltage”≧10V

[0178] If the particle threshold effect is 5V electric field strength,Vbm must be equal to or greater than 25V and Vtm must be equal to orgreater than 5V. In general, the top and bottom magnetic field strengthsmay vary depending on the particle threshold effect and the drivingvoltages set.

[0179] (c) Dual Switching Mode/One Top Permanent Magnetic Layer and OneBottom Switchable Magnetic Layer

[0180] In this embodiment, one permanent magnetic layer is on the top ofthe cell and one switchable magnetic layer is underneath the bottomelectrode layer. The magnetic fields generated by these two magneticlayers are in the opposite direction. Therefore, for example, when themagnetic particles are attracted (pulled) to the top side by the topmagnetic layer, the bottom magnetic layer pushes the particles andassists the particles to migrate toward the top side although themagnetic force between the particles and the bottom magnetic layer maybe negligible. In this alternative design, initially, all top rowelectrodes are also reset to 0V and all bottom electrodes are reset to40V. During reset, all bottom magnetic rows are turned off. As a result,all particles move to the top and a white color is seen from the viewingside.

[0181] When a row is being scanned (scanning row), a driving voltage of40V is applied to the top row electrode and the bottom magnetic layer isturned off. The voltages applied to the bottom center and sideelectrodes are those shown in FIGS. 8A, 8B and 8C. Consequently, thecells may have varied colors as also shown in FIGS. 8A, 8B and 8C.

[0182] When the voltages applied to the bottom center and sideelectrodes are all at 10V or at 10V-40V-10V respectively, in order forthe particles to migrate to the bottom or side electrodes, the followingcondition must be satisfied:

30V>Vtm+“threshold voltage”

[0183] When most of the particles are near or have migrated to theirdestinations, the voltages applied to the top row and bottom center andside electrodes of the scanning row are set to 0V and the bottomswitchable magnetic layer is turned on. The particles at the top areattracted by the magnetic field formed between the particles and the topmagnetic layer, and the particles at the bottom are attracted by themagnetic field formed between the particles and the bottom magneticlayer. As a result, the screening effect is reduced and the particlesare packed tighter and remain at the desired locations.

[0184] For a non-scanned row, the magnetic layers are turned off and 0Vis applied to the top row electrode, which results in all particlesbiased to the top of the cell and remaining at the top of the cell.

[0185] After a row is scanned, that row becomes a scanned row while thenext row is being scanned. For a scanned row, both the top and thebottom magnetic layers are turned on. A 20V is applied to the top rowelectrode of the scanned row. The voltages for the bottom columnelectrode and the two side electrodes vary according to the states beingdriven on the scanning row, thus generating nine possible scenarios asillustrated below. The particles in a scanned row must remain at theirlocations set during the scanning phase.

[0186] 1) In cell A of FIG. 8A, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row. When the column and side electrodes are all at 40V,the particles remain at the top of the electrode.

[0187] When the column and side electrodes are all at 10V, in order forthe particles to remain at the top, the following condition must besatisfied:

Vtm+“threshold voltage”≧10V

[0188] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain at the top, thefollowing condition must be satisfied:

Vtm+“threshold voltage”≧10V

[0189] 2) In cell B of FIG. 8B, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row. When the column and side electrodes are all at 40V,in order for the particles to remain at the bottom, the followingcondition must be satisfied:

Vbm+“threshold voltage”≧20V

[0190] When the column and side electrodes are all at 10V, the particlesremain at the bottom.

[0191] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain covering the bottom,the following condition must be satisfied:

Vbm+“threshold voltage”≧30V

[0192] 3) In cell C of FIG. 8C, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row. When the column and side electrodes are all at 40V,in order for the particles to remain at the side electrodes, thefollowing condition must be satisfied:

Vbm+“threshold voltage”≧20V

[0193] When the column and side electrodes are all at 10V, the particlesremain at the side electrodes.

[0194] When the column and side electrodes are set at 10V-40V-10Vrespectively, the particles remain at the side electrodes.

[0195] Considering all above scenarios, the particle material thresholdand the magnetic field strengths must meet the follow conditions:

Vbm+“threshold voltage”≧30V

Vtm+“threshold voltage”≧10V

30V >Vtm+“threshold voltage”

[0196] In this example, if the particle threshold effect is 5V electricfield strength, Vbm must be equal to or greater than 25V and Vtm must beequal to or greater than 5V; but less than 25V. In general, the top andbottom magnetic field strengths may vary depending on the particlethreshold effect and the driving voltages applied.

[0197] (d) Dual Switching Mode/Two Permanent Magnetic Layers

[0198] In this embodiment, one permanent magnetic layer is on the top ofthe cell and one permanent magnetic layer is undereath the bottomelectrode layer. The magnetic fields generated by these two magneticlayers are in the opposite direction. Therefore, for example, when themagnetic particles are attracted (pulled) to the top side by the topmagnetic layer, the bottom magnetic layer pushes the particles andassists the particles to migrate toward the top side although themagnetic force between the particles and the bottom magnetic layer maybe negligible. In this alternative design, initially, all top rowelectrodes are also reset to 0V and all bottom electrodes are reset to40V. As a result, all particles move to the top and a white color isseen from the viewing side.

[0199] When a row is being scanned (scanning row), a driving voltage of40V is applied to the top row electrode. The voltages applied to thebottom center and side electrodes are those shown in FIGS. 8A, 8B and8C. Consequently, the cells may have varied colors as also shown inFIGS. 8A, 8B and 8C.

[0200] When the bottom center and side electrodes are set at all 10V orat 10V-40V-10V respectively, in order for the particles to migrate tothe bottom or side electrodes, the following condition must besatisfied:

30V>Vtm+“threshold voltage”

[0201] When most of the particles are near or have migrated to theirdestinations, the voltages applied to the top row and bottom center andside electrodes of the scanning row are set to 0V. The particles at thetop are attracted by the magnetic field formed between the particles andthe top magnetic layer, and the particles at the bottom are attracted bythe magnetic field formed between the particles and the bottom magneticlayer. As a result, the screening effect is reduced and the particlesare packed tighter and remain at the desired locations.

[0202] For a non-scanned row, 0V is applied to the top row electrode,which results in all particles biased to the top of the cell andremaining at the top of the cell.

[0203] After a row is scanned, that row becomes a scanned row while thenext row is being scanned. For a scanned row, a 20V is applied to thetop row electrode of the scanned row. The voltages for the bottom columnelectrode and the two side electrodes vary according to the states beingdriven on the scanning row, thus generating nine possible scenarios asillustrated below. The particles in a scanned row must remain at theirlocations set during the scanning phase.

[0204] 1) In cell A of FIG. 8A, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row. When the column and side electrodes are all at 40V,the particles remain at the top of the electrode.

[0205] When the column and side electrodes are all at 10V, in order forthe particles to remain at the top, the following condition must besatisfied:

Vtm+“threshold voltage”≧10V

[0206] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain at the top, thefollowing condition must be satisfied:

Vtm+“threshold voltage”≧10V

[0207] 2) In cell B of FIG. 8B, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row. When the column and side electrodes are all at 40V,in order for the particles to remain at the bottom, the followingcondition must be satisfied:

Vbm+“threshold voltage”≧20V

[0208] When the column and side electrodes are all at 10V, the particlesremain at the bottom.

[0209] When the column and side electrodes are set at 10V-40V-10Vrespectively, in order for the particles to remain covering the bottom,the following condition must be satisfied:

Vbm+“threshold voltage”≧30V

[0210] 3) In cell C of FIG. 8C, a 20V (instead of 40V) is now applied tothe top row electrode, the column and side electrodes may be all at 40V,all at 10V or at 10V-40V-10V respectively, depending on voltages appliedto the scanning row.

[0211] When the column and side electrodes are all at 40V, in order forthe particles to remain at the side electrodes, the following conditionmust be satisfied:

Vbm+“threshold voltage”≧20V

[0212] When the column and side electrodes are all at 10V, the particlesremain at the side electrodes.

[0213] When the column and side electrodes are set at 10V-40V-10Vrespectively, the particles remain at the side electrodes.

[0214] Considering all above scenarios, the particle material thresholdeffect and the magnetic field strengths-must meet the follow conditions:

Vbm+“threshold voltage”≧30V

Vtm+“threshold voltage”≧10V

30V >Vtm+“threshold voltage”

[0215] In this example, if the particle threshold effect is 5V electricfield strength, Vbm must be equal to or greater than 25V and Vtm must beequal to or greater than 5V; but less than 25V. In practice, the top andbottom magnetic field strengths may vary depending on the particlethreshold effect and the driving voltages applied.

[0216] For ease of illustration, it is demonstrated in all of the aboveembodiments that white positively charged magnetic particles are used.It should be understood that the invention is not limited to only thistype of particles. There are many other particle systems, which areuseful for this invention. Such particle systems may include, but arenot limited to:

[0217] 1. Mixture of black particles and white or other coloredparticles in a clear colorless solvent wherein the black particles arecharged and magnetic and the white or other colored particles arenon-charged and non-magnetic; or

[0218] 2. Mixture of black particles and white or other coloredparticles in a clear colorless solvent wherein the black particles arecharged and magnetic and the white or other colored particles arenon-magnetic and also carry charge opposite from the black particles; or

[0219] 3. Mixture of black particles and white or other coloredparticles in a clear colorless solvent wherein the black particles arecharged and magnetic and the white or other colored particles arenon-magnetic and carry the same charge as the black particles but at adifferent level.

[0220] As demonstrated, all of the alternative designs of the inventionmay be readily implemented. The field strengths of the magnetic layersmay vary depending on the particle material threshold effect and thedriving voltages applied during operation. The various designs withinthe scope of this invention have many advantages. For example, itreduces the threshold requirement because of the presence of themagnetic layer(s). When the designs have two magnetic layers, themagnetic field is turned on when the particles are near the electrodes.This feature reduces the switching time because the magnetic fieldcontinues to attract the particles during the non-scanning phase whenother rows are being scanned. The electric field may be turned offbefore the “screening effect” takes place. The magnetic field continuespulling and packing the particles which significantly improves thecontrast ratio.

[0221] It is therefore wished that this invention to be defined by thescope of the appended claims as broadly as the prior art will permit,and in view of the specification.

What is claimed is:
 1. An electromagnetophoresis display, comprising a)a top electrode layer and a bottom electrode layer, at least one ofwhich is transparent; b) an array of cells filled with charged andmagnetic particles dispersed in a solvent; and c) at least one magneticlayer.
 2. The display of claim 1 which has an up/down traditionalswitching mode and said one magnetic layer is switchable and is placedwith the bottom electrode layer.
 3. The display of claim 1 which has anup/down traditional switching mode and two magnetic layers.
 4. Thedisplay of claim 3 wherein one of said magnetic layer is placed with thetop electrode layer and the other is placed with the bottom electrodelayer.
 5. The display of claim 4 wherein both magnetic layers areswitchable.
 6. The display of claim 4 wherein the top magnetic layer ispermanent and the bottom magnetic layer is switchable.
 7. The display ofclaim 4 wherein both magnetic layers are permanent.
 8. The display ofclaim 1 which has a dual switching mode whereby the bottom electrodelayer comprises a center electrode and two side electrodes.
 9. Thedisplay of claim 8 which has a dual switching mode and said one magneticlayer is switchable and is placed with the bottom electrode layer. 10.The display of claim 8 which has a dual switching mode and two magneticlayers.
 11. The display of claim 10 wherein one of said magnetic layeris placed with the top electrode layer and the other is placed with thebottom electrode layer.
 12. The display of claim 11 wherein bothmagnetic layers are switchable.
 13. The display of claim 11 wherein thetop magnetic layer is permanent and the bottom magnetic layer isswitchable.
 14. The display of claim 11 wherein both magnetic layers arepermanent.
 15. The display of claim 1 wherein said magnetic chargedparticles are of the white color and dispersed in a black or coloredsolvent.
 16. The display of claim 1 wherein said particles are a mixtureof black particles and white or other colored particles in a clearcolorless solvent, said black particles being charged and magnetic andsaid white or other colored particles being non-charged andnon-magnetic.
 17. The display of claim 1 wherein said particles are amixture of black particles and white or other colored particles in aclear colorless solvent, said black particles being charged and magneticand said white or other colored particles being non-magnetic andcarrying charge opposite from the black particles.
 18. The display ofclaim 1 wherein said particles are a mixture of black particles andwhite or other colored particles in a clear colorless solvent, saidblack particles being charged and magnetic and said white or othercolored particles being non-magnetic and carrying the same charge as theblack particles but at a different level.
 19. The display of claim 1wherein said at least one magnetic layer generates a magnetic field. 20.The display of claim 19 wherein the strength of said magnetic field isdetermined by the particle threshold effect and the driving voltagesapplied to said electrode layer.
 21. The display of claim 1 wherein saidmagnetic particles are paramagnetic, ferromagnetic, antiferromagnetic orferrimagnetic particles.
 22. The display of claim 1 wherein saidmagnetic particles are prepared from materials selected from a groupconsisting of gamma ferric oxide, acicular magnetite, cobalt-modified oradsorbed ferric oxide, berthollide ferric oxide, chromium dioxide,metals or alloys and organic polyradicals.
 23. The display of claim 22wherein said metal or alloy is stainless steel, Fe—Co, Fe—Ni, Fe—Co—Ni,Co—Ni, Co—Cr or Fe—Co—V alloy.
 24. The display of claim 22 wherein saidorganic polyradical is selected from a group consisting of polymers withorganic radicals in the side chain, main-chain conjugated polymers withorganic radicals, two dimensional polyradicals, polymers containingparamagnetic metalloporphyrins as side chains and polymers containingparamagnetic metal ions in the main chain.
 25. The display of claim 24wherein said paramagnetic metal ion is Cu(II), Ni(II), Mn(II) or VO(II).26. The display of claim 1 wherein said magnetic particles are particlesmagnetized by overcoating or microencapsulating with a magnetic shell.27. The display of claim 26 wherein said magnetic shell is formed from amaterial selected from a group consisting of gamma ferric oxide,acicular magnetite, cobalt-modified or adsorbed ferric oxide,berthollide ferric oxide, chromium dioxide, metals or alloys and organicpolyradicals.
 28. The display of claim 27 wherein said organicpolyradical is selected from a group consisting of polymers with organicradicals in the side chain, main-chain conjugated polymers with organicradicals, two dimensional polyradicals, polymers containing paramagneticmetalloporphyrins as side chains and polymers containing paramagneticmetal ions in the main chain.
 29. The display of claim 28 wherein said ametal or alloy is selected from a group consisting of Ni, Cu, Co, Fe,Cr, Fe—Co, Fe—Ni, Fe—Co—Ni, Co—Ni, Co—Cr and Fe—Co—V alloys.
 30. Thedisplay of claim 29 wherein said metal or alloy shell is coated onto theparticles by sputtering, vacuum deposition, electrodeposition,electroplating or electroless plating.
 31. The display of claim 26wherein said magnetic shell is a magnetic polymer shell coated onto theparticles by a microencapsulation processes.
 32. The display of claim 31wherein said magnetic polymer shell is formed of a polymer selected froma group consisting of polymers with organic radicals in the side chain,main-chain conjugated polymers with organic radicals, two dimensionalpolyradicals, polymers containing paramagnetic metalloporphyrins as sidechains and polymers containing paramagnetic metal ions in the mainchain.
 33. The display of claim 32 wherein said paramagnetic metal ionis Cu(II), Ni(II), Mn(II) or VO(II).
 34. The display of claim 31 whereinsaid microencapsulation process is phase separation, simple and complexcoacervation, interfacial polymerization or crosslinking, in-situpolymerization or crosslinking, phase separation, spray drying,fluidized bed drying, orifice or in-liquid curing or hardening.
 35. Thedisplay of claim 1 wherein said magnetic particles are microcapsulescontaining magnetic materials dispersed in a polymeric matrix.
 36. Thedisplay of claim 35 wherein said microcapsules further comprise apigment or dye.
 37. The display of claim 36 wherein said pigment iswhite TiO₂ or ZnO.
 38. The display of claim 36 wherein said pigment iscolored.
 39. The display of claim 1 wherein said magnetic particles arecolored or black.
 40. The display of claim 39 wherein said blackmagnetic particles are prepared from gamma ferric oxide, acicularmagnetite, cobalt-modified or adsorbed ferric oxide, berthollide ferricoxide or chromium dioxide.